Japan launched a massive military rescue operation Saturday after a giant, quake-fed tsunami killed hundreds of people and turned the northeastern coast into a swampy wasteland, while authorities braced for a possible meltdown at a nuclear reactor.Prime Minister Naoto Kan said 50,000 troops would join rescue and recovery efforts following Friday's 8.9-magnitude quake that unleashed one of the greatest disasters Japan has witnessed _ a 23-foot (7-meter) tsunami that washed far inland over fields, smashing towns, airports and highways in its way. The official death toll stood at 413, while 784 people were missing and 1,128 injured. In addition, police said between 200 and 300 bodies were found along the coast in Sendai, the biggest city in the area near the quake's epicenter. An untold number of bodies were also believed to be buried in the rubble and debris. Rescue workers had yet to reach the hardest-hit areas.Adding to the worries was the damage at the Fukushima Dai-ichi nuclear power plant, where two reactors had lost cooling ability. Because of the overheating, a meltdown was possible at one of the reactors, said Ryohei Shiomi, an official with Japan's nuclear safety commission. But even if there was a meltdown, it wouldn't affect people outside a six-mile (10-kilometer) radius, he said. Most of the 51,000 residents living within the danger area had been evacuated, he said. More than 215,000 people were living in 1,350 temporary shelters in five prefectures, or states, the national police agency said. Since the quake, more than 1 million households have not had water, mostly concentrated in northeast. «Most of houses along the coastline were washed away, and fire broke out there,» he said after inspecting the quake area in a helicopter. «I realized the extremely serious damage the tsunami caused.» The region continued to be jolted by tremors, even 24 hours later. More than 125 aftershocks have occurred, many of them above magnitude 6.0, which even alone would be considered strong, according to a report of the Associated Press.